Seems like asteroids could have a lot of confounders, such as solar wind and CMEs, the gravity of undiscovered other bodies, impacts with other bodies, gas pocket eruptions, and more. So looking for small departures from strict predictions won’t necessarily establish a fifth force.
I'm thinking the same as you. There could be an explanation that doesn't involve a massive overhaul of current theory. For instance, does the asteroid have a metal core that is affected by magnetic fields of planets or other asteroids? Are there other bodies in its vicinity we haven't discovered yet, that could alter its orbit either magnetically or gravitationally? Are there radioactive materials? these are forces that we already know exist (gravity, electromagnetism and nuclear), we just don't know if they are nearby.
If there is an unknown "fifth" force at work here, I vote we call it "the Schwartz"!
I was thinking they were evident at the molecular level- gravity magnetism strong weak.